Introduction

To setup the FX3U-232ADP-MB Modbus module, it is necessary to initially configure the serial communication settings. this is relatively straight forward but there is a small issue to take care of when using GX IEC Developer.

Design Considerations

To configure FX3U-232ADP-MB Modbus settings it is necessary to move certain values into a series of special data registers. Logically the 2 examples below are identical but only the first example actually works.

Example 1 – Using enable EN – ENO chain

Actual code generated for network 1:

  • (MAIN_PRG_LD [PRG])
  • (MELSEC code of NVV #1 in MAIN_PRG_LD)
  • (* code generated at 02/09/2009 16:51:45, 22 steps, 34 steps for the whole object *)

Example 2 – Using parallel enable branches

  • (MAIN_PRG_LD1 [PRG])
  • (MELSEC code of NVV #1 in MAIN_PRG_LD1)
  • (* code generated at 02/09/2009 16:51:46, 28 steps, 40 steps for the whole object *)

Actual code generated for network 1:

  • (MAIN_PRG_LD1 [PRG])
  • (MELSEC code of NVV #1 in MAIN_PRG_LD1)
  • (* code generated at 02/09/2009 16:51:46, 28 steps, 40 steps for the whole object *)

Summary

As you can see, example 1 creates code with LD instruction followed by several MOV instructions. Example 2 creates LD instructions for every MOV instruction. For successful completion of the Modbus communications setup, example 1 is the only that works.

Further Information

For further information, please refer to the FX3U-232-ADP-MB user manual and GX IEC Developer help files or contact our support desk (support@adroit.co.za).

You can download Tip in PDF format here.

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